Insulating needs for poured concrete

[PTB]

Hello,

I'm in the process of building a 1500+ sq. ft. garage that is constructed of poured concrete walls of various heights from approximately 3 feet that is stepped up to approximately 8 feet. The reason for the height difference is the structure is built into a small hill. The balance of the overall garage height is built with lumber using 2x6" studs, OSB wall exterior sheathing, engineered truss roof with asphalt shingles and fiberglass insulation in walls and ceiling. Interior ceiling height is 12' with sheetrock on the lumber only. Exterior concrete walls are insulated with 2" foam board from footing to grade.

My question is will just having the 2" foam board and the earthen fill against it be sufficient to insulate the concrete for HVAC? This will be a hobbyist / vehicle storage garage for all season use. It is located in Dutchess County, New York where we experience cold winters and hot, humid summers. I know from reading that concrete itself has no R value but I'm being told interior insulation, which would involve constructing wood studded walls to install fiberglass insulation and sheetrock, may not have a cost benefit and the the R10 rating of the exterior foam board would be enough for the application.

Thank you in advance for your assistance!

 

[Beemer]

My full basement has 10" concrete walls, 2" insulation for the top few feet and just 18" wall exposed above grade which have four basement windows.

We have, or used to have, four seasons.

We can get the basement near 80 degrees with a smallish wood stove in the winter but in the same time frame without the stove burning it never goes below 65 degrees. In the hot summer it might be 70 degrees down there.

That may not tell the answer you are looking for but it shows me that the earth insulates, even the frozen part (our code frost line is 42" but having seen foundations built in the winter I can't recall seeing frozen soil more than a couple feet down.

Edit to clarify. The insulation is only on the outside of the wall below grade, not above the ground.

 

[billconner]

I'd guess you'll get some slight condensation on the portion of the concrete wall above grade if you turn the heat down on very cold days. 2" of foam is about half the code requirement in your area.

 

[pcmeiners]

Use EPS foam boards instead of XPS as to moisture resistance; moisture traveling through insulation lowers stated R value. Check on Facebook's "market place" for insulation. 2" is more than many garages have, more the better.

 

[PTB]

Use EPS foam boards instead of XPS as to moisture resistance; moisture traveling through insulation lowers stated R value. Check on Facebook's "market place" for insulation. 2" is more than many garages have, more the better.

Thank you for the marketplace advice. Did not think of that as I'm always on it looking at other stuff.

 

[PTB]

I'd guess you'll get some slight condensation on the portion of the concrete wall above grade if you turn the heat down on very cold days. 2" of foam is about half the code requirement in your area.

Interesting as the town did not care whether or not I insulated at all as it is not considered living space. I plan to be out there all year round most days. Thank you!

 

[PTB]

My full basement has 10" concrete walls, 2" insulation for the top few feet and just 18" wall exposed above grade which have four basement windows.

We have, or used to have, four seasons.

We can get the basement near 80 degrees with a smallish wood stove in the winter but in the same time frame without the stove burning it never goes below 65 degrees. In the hot summer it might be 70 degrees down there.

That may not tell the answer you are looking for but it shows me that the earth insulates, even the frozen part (our code frost line is 42" but having seen foundations built in the winter I can't recall seeing frozen soil more than a couple feet down.

Your info is most helpful. There is so much info out there it can sometimes cause more questions than answers.

 

[billconner]

Interesting as the town did not care whether or not I insulated at all as it is not considered living space. I plan to be out there all year round most days. Thank you!

Usually the code requirement for insulation is based on if your heating and/or cooling it.

 

[pcmeiners]

"Thank you for the marketplace advice. Did not think of that as I'm always on it looking at other stuff."

Same here, half the time I forget to look on FaceB or Ebay, it is called impulse buying or how to throw your money away.

"There is so much info out there it can sometimes cause more questions than answers."

And far more cost (generally) then expected, especially in this forum, we love to spend OP's money

 

[ConCretin]

2" of rigid insulation is fine. You might consider Z furring for attaching the insulation to the wall. It can also be used to attach wall sheathing.



I ran the Z furring horizontally and left a gap to act as a raceway for wiring, air piping, etc. I covered the chase with removable plywood covers to accommodate changes and additions.